Nice images.

gamedever is correct - whether you use a self-lit Image Environment Sphere OR you use an Image Based Light, either will supply global illumination data for use with IDL. Only the IES will provide reflection data for the Reflect node - IBL will not do that. So that is a difference worth considering. But this is not important for dry skin. It is important for wet skin if you bother to use reflection on the skin shader, which I have not shown anybody how to do, but you might figure it out yourselves. (Do any of you remember my muddy/wet skin shader demos? I forgot to publish that shader.)

Anyway, there is indeed a very big difference between IDL and AO. AO merely darkens things, and sometimes darkens the wrong things. IDL may darken or lighten things - this is the key - when you put your hand near your cheek, your cheek becomes brighter and more red if the hand is angled correctly - only IDL handles this. In other situations, the hand will merely shadow the cheek, as simulated by AO.

So, to fully appreciate the impact of IDL on one of these "isolated figure" scenes, you have to take into account whether or not the ground is well lit, and also consider the pose. In gamedever's last image, we cannot clearly see armpits and the thighs are far apart. Change that pose to reveal the mutual occlusion of arm to torso, or thigh to thigh, and you will see a big difference between IBL+AO versus IBL+IDL.

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)